Coloring of magnesium and alloys thereof



Patented Jan. 23, 1951 COLORING F MAGNESIUM AND ALLOYS THEREOF Paul R.Cutter, Matawan, N. 3., assignor to Consolidated Vultee AircraftCorporation, San

Diego, Calif., a corporation of Delaware No Drawing. Application July 9,,1946, Serial No. 682,315

21 Claims. (01. 204-36) This invention relates to an improved method ofcoloring magnesium and magnesium-base alloy articles and moreparticularly to the coloring of magnesium and magnesium-base alloyarticles which have been subjected first to electrochemical treatment.

Magnesium and magnesium-base alloys must be given protective coatings topermit their widespread use. These coatings must afford protectionagainst corrosion, abrasion and fire. As is known in the art aprotective coating can be applied to magnesium and magnesium-base alloysby electrochemical processes wherein the articles made of such metalsare anodically treated in an electrolytic cell containing a suitableelectrolyte and with the articles serving as the anode.

It is an object of this invention to treat such protective coatings fordecorative effect.

Another object of this invention is to provide a method of coloringmagnesium and magnesium-base alloy articles which effects a uniformityof coverage of the articles treated and in which the coating produced isparticularized by its high resistance to fading and by its sealingeifects.

A further object of the invention is to provide an improved method ofcoloring electrolytically treated magnesium utilizing a mordant bathwhich effects permanent retention and adherence of the dye.

A still further object of the invention is to provide an improved methodof coloring magnesium or magnesium-base alloy articles wherein after thearticle has been subjected to electrolytic treatment it is dipped in animproved type of mordant bath before being dipped in the dye bath.

Other objects and features of this invention will be readily apparent tothose skilled in the art from the following specification.

In carrying out the present invention the articles formed of magnesiumor magnesium-base alloys which are to be colored are subject to anodictreatment in an electrolytic cell, using as an electrolyte a solution ofa silicate and a caustic to which may be added a quantity of an organiccompound such as phenol. The articles to be coated serve as the anode.Alternating current preferably of 60 cycles and of a density of 20 to 30amperes per sq. ft., or direct current of a density of to 20 amperes, ispassed through the electrolyte for a period of 10 to 30 minutes. Thistreatment effects a hydrated oxide protective coating which it has been.fQ lIld is highly resist.-

2 ant to corrosion and abrasion and further is highly compatible withpaint.

After the protective coating has been formed on the magnesium ormagnesium-base alloy surface the coated metal is treated according tothe present invention to produce a desired color thereon. After removalfrom the electrolytic cell the articles being processed are immersed ina mordant bath containing an aqueous solution of two water-soluble saltsof acetic acid of which one is ammonium acetate and the other a metallicsalt. The salts of acetic acid Which are best adapted for use in thepresent invention with the salt, ammonium acetate, are the metallicsalts, aluminum acetate, lithium acetate, zirconium acetate, strontiumacetate and barium acetate. In general, a satisfactory mordant bath willcomprise a concentration of from about .1% to about .4% of the ammoniumacetate and from about .1 to about .6% of one of the metallic aceticacid salts named immediately above.

The ammonium acetate acts as a stabilizing agent and serves to hold themetallic acetic acid salt used with it in solution by providing a commonion-acetate to discourage decomposition of the salt and precipitation ofthe metal as an oxide in the mordant bath. The ammonium acetate has aneutral action on the anodic protective coating provided on the metalsurface and will not injure it, and it further acts as a buffer orstabilizer to stabilize the pH of the mordant bath.

After the article has been dipped in the mordant solution and removedtherefrom the surface thereof will retain a film of the metallicacetate. The acetate ion thereof then reacts with the hydrated magnesiumoxide finish freeing the metallic ion and allowing it to hydrolyze intoa hydrated metallic oxide on the surface of the anodized magnesiumarticle. The hydrated metallic oxide deposited is in the form of a geland will be retained by the pores in the anodized coating. Thisprovision of a highly hydrolyzed metallic oxide on the anodized articlehas a sealing efiect though it probably does not fully seal the anodizedsurface but does to a sufiicient degree as to be beneficial. The mordantbath is held at a temperature of from F. to F. and the magnesium articleis held immersed for about one minute. Maintaining the temperature ofthe bath at the relatively high temperatures named is primarily for thepurpose of reducing the length of time that it is necessary to keep thearticle being processed immersed and further to preheat the articlewhereby when it is removed from the mordant bath there will be sumcientheat absorbed by the article to effect a quick evaporation of most ofthe water film and a neutralization of the acetate ions, thus leavingthe metal of the acetic salt as a hydrolyzed oxide on the surface of thearticle where it serves as a mordant. It has been foundthat the time ofimmersion in the mordant bath should not exceed much more than oneminute or a stripping action will occur which may break through theanodized coating at sharp edges.

From the mordant bath the article-is taken to a dye bath. It is to benoted that the article is moved after a brief pause to allow-partialdrying of the mordant treated surface, directly to the dye bath from themordant bath, there is no water rinse for to so treat the article wouldwash away metallic ions before they had an opportunity to hydrolyze. Thedye bath used in the present invention employs water-soluble organicdyes which should preferably be either an acid or a chrome type dye,such as azo dyes or azo dyes containing chromium. The following areexamples of dyes that maybe used:

Neolan Blue 2G v(Cone) o ack e 38- Hi Cens- Tartraz ine Diamond RedBHA'Extr. Conc. Anthraquinone Blue B1 T The pH'value of the dye bath,usually ranging from 5.0 to 8.5 depending on the dye used, willbe'stabilized by contaminations carried over from the mordant bath. Theconcentration of the dyes in the aqueous bath is from about 1 gram toabout 5 grams per liter, and in general about 2 grams per liter is mostsuitable. Bath tempera- ;tures of from about 65 C. to 80 C. aresatisfactory. The parts are immersed from one to two minutes if pastelshades are desired and from three to ten minutes for the darker shades,depending on the dye used. On immersion of the mordant treated anodizedarticle into the dye bath a reaction occurs between the hydratedmetallic oxideand the dye to form insoluble color lakes. These colorlakes fixed upon the processed article impart to it a permanent color.

Imparting a color to magnesium or magnesium-base alloys in the mannerabove described eifects a greater depth of color than by other methodsknown. iChe final coating is uniform and very highly resistant to fadingin sunlight, and furthermore at least a partial sealing of the anodiccoating is effected.

The following example illustrates the method of coloring of articlesmade of magnesium 'or -magnesium-base alloysaccording to the present 1invention.

Example Panels made of magnesium and magnesium- For this an electrolytewas 4 tic base and a soluble silicate to which was added an organiccompound. The composition of this bath may vary as follows:

By weight Sodium hydroxide 23 to 25% -."1"'"'f"'"---.- 7".-.'T "-7-" toSodium silicates (water glass) 2.5 to 3.5%

The temperature of the electrolyte was maintained at F. With themagnesium articles serving as the anode, direct current of a density ofi5 amperes per sq. ft. was passed through the electrolyte for a periodof 20 minutes.

The anodic coating formed on articles subjected to treatment as above iscorrosion and abrasion resistant and comprised a hard, dense coating ofhydrated magnesium oxide.

The anodized panels were then transferred to the mordant bath, anaqueous solution having therein:

Grams per liter 5% of aluminum acetate 5 3% of ammonium acetate 3 Thismordant bath was held at a temperature of between 180 to F. Afterimmersion for about one minute the panels were removed and after a briefpause to allow for drainage and partial drying, they were directlytransferred to the dye bath.

The dye bath was comprised of an aqueous-solution of 2% anthraquinoneBlue BN. The temperature of the bath was 75 C. and the panels were heldin this dye bath for about 3 minutes. This resulted in the articlesbeing dyed a royal blue.

The foregoing example has been 'by way of illustration only and it isunderstood that it is not to be construed as limiting the invention.

Utilizing the method above described coatings having practically anydesired shade of color are obtainable. The coatings provided arehomogenous and uniform and afford a very high degree of protectionagainst mechanical abrasion and corrosion.

Having particularly described and pointed out my invention, I claim:

1. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises briefly immersing the electrolytically coated article in aheated mordant bath consisting of an aqueous solution of a water-solublemetallic salt of acetic acid, in a proportion between 1 gram and about 6grams per liter, and a stabilizing agent, in a proportion between 1 gramand about 4 grams per liter for preventing the decomposition of saidwater-soluble metallic salt of acetic acid, removing the article fromthe mordant bath, permitting it to partially dry, and next immersing thearticle in an aqueous solution of a lake-forming dye.

2. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises immersing the electrolytically coated article for a briefperiod of time in a heated mgrdant bath consisting of an aqueoussolution of aluminum acetate, in a proportion between 1 ram and about 6grams per liter, and a stabilizing agent, in a proportion between 1 gramand about 4 grams per liter,'for preventing the decomposition of saidaluminum acetate, removing the article from the mordant bath, permittingit to partially dry, and next immersing the article in an aqueoussolution of a lake-forming dye.

3. A process of coloring electrolytically produced hydrated oxidecoatings on articles of mag nesium and magnesium-base alloys, whichcomprises immersing the electrolytically coated articles for about oneminute in a heated mordant bath consisting of an aqueous solution ofammonium acetate, in a proportion between 1 gram and about 4 grams perliter, and a water-soluble me-I ticle for about one minute in a, heatedmordant? bath consisting of an aqueous solution of ammonium acetate in aproportion between about I gram and about 4 grams per liter and aluminumacetate in the proportion between about 1 gram and about 6 grams perliter, removing the articlefrom the mordant bath, permitting it topartially dry, and nextimmersing the article in an aqueous solution of awater-soluble lake-forming dye.

duced hydrated oxide coatings on articles of magnesium and"magnesium-base alloys, which comprises immersing the electrolyticallycoated article for about one minute in an aqueous solution of ammoniumacetate in a proportion between about 1 gram and about 4 grams per literand aluminum acetate in a proportion of between about 1 gram and about 6grams per liter, at a temperature between 180 to 190 F., removing thearticle from the aqueous solution, permitting it to partially dry, andnext immersing the article i an aqueous solution of an azo dyecontaining chromium.

6. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises immersing the electrolytically coated article for a briefperiod of time in a heated mordant bath consisting of an'aqueoussolution containing about 3 grams per liter of ammonium acetate andabout 5 grams per liter of aluminum acetate, removing the article fromthe mordant bath, permitting it to partially dry, and next immersing thearticle in an aqueous solution of a water-soluble dye.

7. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises immersing the electrolytically coated arcle for about oneminute in an aqueous solution of ammonium acetate, in a proportionbetween 1 gram and about 4 grams per liter, and a watersoluble metallicsalt of acetic acid in a proportion between 1 gram and about 6 grams perliter, at a temperature between 180 to 190 'F., removing the articlefrom the aqueoussolution, permitting it to partially. dry, and nextimmersing the article in an aqueous solution of a water-soluble dye.

8. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises immersing the electrolytically coated article for about oneminute in an aqueous solution containing about 3 grams 'per liter ofammonium.

5. A process of coloring electrolytically proacetate and about 5 gramser liter of aluminum 9. A method of coloring electrolytically pro ducedhydrated oxide coatings on articles of mag- "nesium and magnesium-basealloys, comprising immersing the electrolytically coated article forabout one minute in a mordant bath heated to a temperature of between180 to 196 F., and

consisting of an aqueous solution containing about 3 grams per liter ofammonium acetate and about 5 grams per liter of aluminum acetate wherebya film is provided upon the surface of the article which reacts with thehydrated oxide coating to deposit hydrated aluminum oxide, re-

moving the article from the mordant bath, permitting it to partiallydry, and next immersing the article in an aqueous solution of an organicacid type dye, which dye is adapted to react with the hydrated aluminumoxide to form an insoluble color lake.

10. A method of producing a colored corrosion and abrasion resistantcoating upon articles formed of magnesium and magnesium-base alloys,consisting of electrolytically treating the article to be coated in anelectrolyte composed of an aqueous solution of sodium hydroxide, 22 to25% by weight, sodium silicate. 2.5 to 3.5% by weight and phenol .2. to'.3% by weight, briefly immersing the electrolytically coated article ina heated mordant bath comprising an aqueous solution :of ammoniumacetate, in a proportion between 1 gram and about 4 grams per liter, and

water-soluble metallic salt of acetic acid, in a "mersing the article inan aqueous solution of a water-soluble dye.

proportion between 1 gram and about 6 grams per liter, removing thearticle from the mordant bath, permitting it to partially dry, and nextimll. A method of producing a colored corrosion and abrasion resistantcoating upon articles formed of magnesium and magnesium-base alloys,consisting of electrolytically treating the article to be coated in anelectrolyte composed of sodium hydroxide, 22 to 25% by weight, sodiumsilicate, 2.5 to 3.5% by weight and phenol, .2 to .3% by weight,immersing the electrolytically coated article for about one minute in amordant bath heated to a temperature of between 18 to F., and compriisngan aqueous solution of ammonium acetate in a proportion between about 1gram and about 4 grams per liter and water soluble metallic salt ofacetic acid taken from the group consisting of aluminum acetate, lithiumacetate, zirconium acetate, strontium acetate and bariumacetate, in aproportion between 1 gram and about 6 grams per liter, removing thearticle from the mordant bath, permitting it to partially dry, and nextimmersing the article in an aqueous solution of a lake-forming dye.

12. A method of producing a colored corrosion and abrasion resistantcoating upon articles -formed of magnesium and magnesium-base alloys,consisting of electrolytically treating the article to be'coated in anelectrolyte composed of an aqueous solution of sodium hydroxide, 22 to25% by weight, sodium silicate, 2.5 to 3.5% by weight and phenol, .2 to3% by weight, immersing the electrolytically coated article for aboutone minute in a heated mordant bath comprising an aqueous solutioncontaining about 3 grams p r liter of ammonium a etate a d a out 5 it topartially dry, and next treating the article in an aqueous solution. ofa water-soluble dye.

13. A method of producinga colored corrosion and abrasion resistantcoating upon articles formed of magnesium and magnesium-base alloys,consisting successively of electrolytically treating the article to becoated in an electrolyte composed of an aqueous solution of sodiumhydroxide, 22 to 25% by weight, sodium silicate, 2.5 to 3.5% by weightand phenol, .2 to .3% by weight, immersing the electrolytically coatedarticle for about one minute in a mordant bath comprising an aqueoussolution of about 3 grams per liter of ammonium acetate and about .5grams per liter of aluminum acetate, at a temperature between 180 to 190F., removing the article from the mordant bath, permitting it topartially dry, and next immersing the article in an aqueous solution ofan organic acid type water-soluble dye.

14. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises immersing the electrolytically coated article for about oneminute in an aqueous solution of ammonium acetate in a proportionbetween about 1 gram and about 4 grams per liter and aluminum acetate ina proportion of between about 1 gram and about 6 grams per liter, at atemperature between 180 to 190 F., removing the article from the aqueoussolution, permitting it to partially dry, and next immersing the articlein an aqueous solution of an azo dye containing chromium, the dyeconcentration being between about 1 gram and 5 grams per liter.

15,. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises immersing the electrolytically coated article for about oneminute in a mordant bath consisting of an aqueous solution containingabout 3 grams per liter of ammonium acetate and about 5 grams per literof aluminum acetate, at atemperature between 180 to 190 F., removing thearticle from the mordant bath, permitting it to partially dry, and nextimmersing the article in an aqueous solution containing about 2 gramsper liter of a water-soluble dye.

16. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises immersing the electrolytically coated article for about oneminute in an aqueous solution of ammonium acetate in a proportionbetween about 1 gram and about 4 grams per liter and aluminum acetate ina proportion of between about 1 gram and about 6 grams per liter, at atemperature between 180 to 190 F., removing the article from the aqueoussolution, permitting it to partially dry, and next immersing the articlein an aqueous solution containing an organic acid type dye in aproportio between about 1 gram and 5 grams per liter, the solution beingmaintained at a temperature betweenabout 65 C. and about 80 C.

17. A process of coloring electrolyticallynprm duced hydrated oxidecoatings on articles of magnesium and magnesiumbase alloys, whichcomprises immersing the electrolytically coated article for about oneminute in an aqueous solution containing about 3 grams per liter ofammonium acetate and about 5 grams per liter of aluminum acetate, at atemperature, between :8 -.to .-removing the article .from the aqueoussolution, ;permitting it to partially dry, and next immersing thearticle in an aqueous solution containing .an-organic acid type dye ina'proportionbetween.about 1 gram and 5 grams per liter, the solutionbeing maintained at a igemperature between about 65 C. and about 18. Aprocess of coloring electrolytically -PIO- duced hydrated oxide coatingson articles of magnesium and magnesium-base alloys, which comprisesimmersing the electrolytically coated article for a short period of timein a heated mordant bath consisting of an aqueous solution of awater-soluble metallic salt of acetic acid taken from a group consistingof aluminum acetate, lithium acetate, zirconium acetate, strontiumacetate, and barium acetate, in a proportion of between 1 gram and about6 grams per liter, and a stabilizing agent for preventing thedecomposition of said water soluble metallic salt of acetic acid, in aproportionof between 1 gram and about 4 grams per liter, removing thearticle from the mordant bathand permitting'it to partially dry, andnext immersingthezarticle in an aqueous solution of a-lake-forming dye.

19. A process of coloring-electrolytically'produced hydrated oxidecoatings on articles-of magnesium and magnesium-base alloys, whichcomprises immersing the-electrolytically coatedarticle for about oneminute in a heated mordant bath and consisting of .an aqueous solutionof a water-soluble metallic :salt-ofacetic acid taken from a groupconsisting of aluminum acetate, lithium acetate, zirconium acetate,strontium acetate, and barium acetate, in a-proportionoi between-1 gramand about-6 grams per liter, and

ammonium acetate in a proportion of between 1 gram and about 4 grams perliter, removing the article from the mordant bath and permitting it topartially dry, and next immersing the article in an aqueous solution ofa lake-forming dye.

20. A process of coloring electrolytically produced hydrated oxidecoatings on articles of magnesium and magnesium-base alloys, whichcomprises immersing the electrolytically coatezl article for about oneminute in a mordant bath heated to a temperature of between 180 to 190and consisting of an aqueous solution of about 5 grams per liter of awater-soluble metallic salt of acetic acid taken from a group consistingof aluminum acetate, lithium acetate, zirconium acetate, strontiumacetate, and barium acetate, and about 3 grams per liter of ammoniumacetate, removing the article from the mordant bath and permitting it topartially dry, and next immersing the article in an aqueous solution ofa lakeforming' dye.

21. A process of coloring electrolytically produced hydrated oxidecoatings on articles of ma nesium and magnesium-base alloys, which comprises immersing the electrolytically coated article for about a minutein a mordant bath heated to a temperature of between 180 to 190 F2, and

consisting .of an aqueous solution of about 5 grams per liter of a watersoluble metallic salt of acetic acid takenirom .a group consisting ofsolution being maintained at a temperature be tween about 65 C. and 80C.

PAUL R. CUTTER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,071,156 Baer Feb. 16, 19372,150,395 Nagata Mar. 14, 1939 2,310,487 De Long Feb. 9, 1943 MonthlyReview, v01. 33, July 1946, page 709.

1. A PROCESS OF COLORING ELECTROLYTICALLY PRODUCED HYDRATED OXIDECOATINGS ON ARTICLES OF MAGNESIUM AND MAGNESIUM-BASE ALLOYS, WHICHCOMPRISES BRIEFLY IMMERSING THE ELECTROLYTICALLY COATED ARTICLE IN AHEATED MORDANT BATH CONSISTING OF AN AQUEOUS SOLUTION OF A WATER-SOLUBLEMETALLIC SALT OF ACETIC ACID, IN A PROPORTION BETWEEN 1 GRAM AND ABOUT 6GRAMS PER LITER, AND A STABILIZING AGENT, IN A PROPORTION BETWEEN 1 GRAMAND ABOUT 4 GRAMS PER LITER FOR PREVENTING THE DECOMPOSITION OF SAIDWATER-SOLUBLE METALLIC SALT OF ACETIC ACID, REMOVING THE ARTICLE FROMTHE MORDANT BATH, PERMITTING IT TO PARTIALLY DRY, AND NEXT IMMERSING THEARTICLE IN AN AQUEOUS SOLUTION OF A LAKE-FORMING DYE.